In recent years, development of a high speed (mechanical) shutter of the digital camera has been actively promoted. It aims is to make possible to obtain clear images by taking a picture of a subject moving at an ultrahigh speed without blurring by making shutter speed high. Generally, opening/closing of shutter is performed by rotating or moving a plurality of blades called as shutter blades, however, in order to obtain a high shutter speed, it is absolutely essential to be lightweight and high slidability so that the shutter blade can correspond to instantaneous motion and stopping. Further, since the shutter blade has a role to shade light by covering the front surface of a photosensitive material such as film or an image sensor such as CCD, CMOS in a state when a shutter is closed, it is desired to have complete light shading performance. Moreover, the shutter blade is desired to be a low reflectivity on the surface of the blade, that is, a high blackness of surface color, in order to prevent an occurrence of leakage of light among each blade when a plurality of shutter blades work while overlapping each other.
As for a fixed diaphragm which is inserted into a lens unit of digital camera and has a role to reduce light intensity to a certain level and transfer the light to an image sensor, the shutter blade is also demanded to have low reflectivity of the surface, that is, a high blackness, because occurrence of light reflection on the surface of a diaphragm gives stray light and impairs sharp images.
Also, in a cellar phone having a photographing function, that is, a cellar camera phone, a compact mechanical shutter has recently begun to be installed in a lens unit, in order to allow taking a picture having fine pixel and high image quality, similarly as in a digital camera. In addition, a fixed diaphragm has been inserted in a lens unit of a cellar phone. A mechanical shutter to be incorporated in the above cellar phone is demanded to work by power saving as compared with a general digital camera. Therefore, demand for weight saving of shutter blades is demanded particularly strong.
To mount a camera module or a lens unit, conventionally parts thereof have been manufactured using adhesives individually. However, in a recent cellar camera phone, when assembling the lens unit, in order to reduce manufacturing cost, it has been required that each of the members such as a lens, a fixed diaphragm, and shutter is manufactured by a reflow step. Accordingly, there has been demanded heat resistance in addition to low surface reflectivity and blackness, for a shutter blade or a fixed diaphragm used for them.
This reflow step has been put to practical application in a manufacturing method for a camera module such as a recent digital camera, a cellar camera phone, aiming at compact sizing, making low profile, and simplification of manufacturing steps. By a practical application of the reflow step, a manufacturing method will be shifted to such a way as all assembly will be made in a wafer state where each of the parts is not separated to each chip unit, and after completion of mounting onto a circuit board using die bonding, solder ball or the like, this is subjected to dicing to a chip size individually to obtain a final product. It should be noted that parts to be used here have been fostered in packaging industry of a semiconductor chip in recent years, and called a wafer level chip size package (hereafter, referred to as WLCSP).
Use of this WLCSP enables to reduce the number of parts and thus is effective to compact sizing, making low profile of a camera module. However, generation of burr or the like at a punched end face causes trouble in lamination of wafers themselves, in assembling a camera module with the WLCSP structure.
In addition, in the case where a flexible printed circuit board (hereafter, referred to as FPC) becomes thinner, light injected from the FPC side at the rear face of an image sensor becomes not neglected, in addition to leakage of light from the front face of the image sensor such as CCD, CMOS. Incident light from the rear face of this image sensor makes a ghost image of a printed circuit of the FPC in a photographing area, which deteriorates quality of a picture image, therefore shading of the leakage of light from the FPC side becomes necessary.
In addition, as a recent trend of a device mounted on an automobile, there is a trend of mounting a monitor using a video camera such as a back view monitor. Also, a fixed diaphragm is used in a lens unit of this video camera monitor, and the surface of the diaphragm is demanded to have low reflectivity and blackness to prevent stray light similarly. In addition, in the lens unit of the in-vehicle video camera, heat resistance is required so as not to impair function, even under high temperature use environment such as the burning sun in midsummer, and heat resistance is required also for a fixed diaphragm material.
On the contrary, a liquid crystal projector, which can watch as a home theater with a large-sized screen, has recently been rapidly becoming popular at home. Since high image quality is intensely demanded in order to enable to enjoy sharp and high contrast images, even in such a bright environment as in a living room, technology to obtain an image quality having high lightness by using a high power light source has been attempted. In an optical system of a projector, a diaphragm device for a light intensity adjusting module (auto-iris), which adjusts light intensity from a lamp light source, has been used inside or on side face of the lens system. In the diaphragm device for the light intensity adjusting module, a plurality of diaphragm blades overlap each other, similarly as in the shutter, to adjust an aperture through which light passes. In such diaphragm blades of diaphragm device for the light intensity adjusting module, low reflectivity on the surface and weight saving are also demanded due to the same reasons as in the case of the shutter blades. At the same time, in the diaphragm blades of diaphragm device for the light intensity adjusting module, heat resistance against heating by irradiation of a lamp light has also been required. That is, it is because impairment of low reflectivity of the blade material by light irradiation causes stray light, making impossible to take a vivid picture image.
In the above-described shutter blade, fixed diaphragm, and a diaphragm blade of a diaphragm device for the light intensity adjusting module, as a light shading plate, the following ones are used in response to required characteristics.
When heat resistance is required, a thin plate of metal such as SUS, SK material, Al, Ti is generally used as a substrate. Although there is a light shading plate in which a metal thin plate itself is used as a light shading plate, this is not preferable when influence of stray light by reflected light from the surface should be avoided because this plate has metallic luster. On the contrary, a light shading plate, in which a black lubricating coating is made on a metal thin plate, has low reflectivity and blackness, but cannot generally be used in high temperature environment because a coated part is inferior in heat resistance. Furthermore, in order to suppress light reflection at the processed end face, after processing to a predetermined shape, a step for black dying processing of the processed end face becomes necessary, which has a problem of increasing manufacturing cost.
Accordingly, in Patent Literature 1, a light shading material in which a hard carbon film has been formed on the surface of a blade material made of a metal such as aluminum alloy has been disclosed. However, even if a hard carbon film is formed on the surface, low reflection characteristics cannot be realized, and generation of stray light by reflected light cannot be avoided. In any of the above cases, when a light shading plate using a metal thin plate as a substrate is used for a shutter blade or a diaphragm blade, there are such problems that torque of a drive motor for driving blades becomes great to increase power consumption, due to its heavy weight; as well as shutter speed cannot be raised; noise generates by contacting of blades themselves; and the like.
On the contrary, there has been proposed a light shading plate using a resin film as a substrate (refer to PATENT LITERATURES 2 and 3). In this PATENT LITERATURE 2, there has been proposed a light shading plate using a matted processed resin film to reduce reflection on the surface, or a film-like light shading plate furnished with lusterless property by forming a large number of fine unevennesses. In addition, in PATENT LITERATURE 3, there has been proposed a light shading film in which a thermosetting resin containing a lusterless paint is coated on a resin film. However, in these proposals, sufficient light shading performance is furnished to a light shading plate, by using a resin film as a substrate, where a black pigment such as carbon black is impregnated in polyethylene terephthalate (PET) or the like, and forming a light shading layer impregnated with a black pigment at the surface of the substrate. That is, sufficient light shading performance cannot be expressed only by a resin film impregnated with a black pigment. In addition, surface reflection or surface glossiness is reduced by impregnation of the black pigment or a matting agent into the light shading layer, however, it cannot prevent stray light generating by light reflection at the end face formed by processing the light shading plate.
As for a light shading plate using a resin film as a substrate, a light shading plate using polyethylene terephthalate (PET) impregnated with a black pigment, as a substrate, is widely used, from the advantages of low specific gravity, cheap cost and flexibility.
However, a PET material has a heat resistance below 150° C. and is weak in mechanical strength such as modulus of elasticity in tension, therefore it cannot be utilized as a diaphragm material for the light intensity adjusting module of a projector, irradiated by a high power lamp light, or a fixed diaphragm material or a shutter material corresponding to the reflow process. In addition, to use it as a blade part of a high speed shutter, thickness of the film has to be reduced corresponding to speeding up of the shutter blade, however, in the case of the resin film produced by impregnating black fine particles therein, thinner film thickness cannot exhibit sufficient light shading performance. In particular, when the thickness becomes 38 μm or less, it cannot be used for a diaphragm for the light intensity adjusting module or a fixed diaphragm, or a shutter blade.
On the other hand, as for a resin film where a black pigment such as carbon black is impregnated in a resin superior in heat resistance, the following proposals have been made. For example, in PATENT LITERATURE 4, a conductive polyimide composition has been disclosed where a black pigment such as carbon black, acetylene black is impregnated in a polyimide resin having high heat resistance. In addition, in PATENT LITERATURES 5 and 6, there have been disclosed a molded body of a conductive polyimide impregnated with a black pigment such as carbon black or graphite. However, in PATENT LITERATURES 4 to 6, there is no description on surface roughness or optical characteristics such as light shading performance, direct reflectance, surface glossiness of the film and thus they cannot be evaluated as a light shading film.
In addition, with progress of compact sizing and thinning of a digital camera and a cellar camera phone, compact sizing and thinning have been required also for component parts to be mounted, in recent years. Accordingly, the present inventors have proposed a heat resistant light shading film consisting of a resin film substrate (A) having a heat resistance of 200° C. or higher, a Ni-type metal film (B) having a film thickness of 50 nm or more formed at one or both surfaces thereof by a sputtering method, and a Ni-type oxide film (C) with low reflectivity formed thereon by a sputtering method, and heat resistant light shading film having a surface roughness (arithmetic average height Ra) of 0.1 to 0.7 μm (refer to PATENT LITERATURE 7). This allowed to make the heat resistant light shading film more superior in light shading performance, heat resistance, slidability, low surface glossiness, and electric conductivity, as compared with a conventional one.
However, there has been strong requirement for a fixed diaphragm and a shutter blade, which are component parts of a lens unit in a camera module, in particular, to have a thickness of 25 μm or less, and such a shutter blade material or a fixed diaphragm material has become essential that has thin film and is superior in heat resistance, highlight shading performance, low surface glossiness, and blackness.
In PATENT LITERATURES 2 and 3, a resin film with a thickness of 25 to 250 μm is used as a substrate, and thus it is not suitable for a fixed diaphragm or a shutter blade for a digital camera or a cellar camera phone, where a film thickness of 25 μm or less is desired. On the other hand, although PATENT LITERATURE 6 has shown Example of a film thickness of about 25 μm, surface thereof is not roughened, and, in PATENT LITERATURES 4 and 5, there have been no description on film thickness.
Further, in a fixed diaphragm or a shutter blade to be used in a digital camera or a cellar camera phone, or a diaphragm blade for the light intensity adjusting module of a projector, a light shading plate, which is processed to a desired shape by machining, is used, and since the processed end face is arranged on a light passage, in the case of high reflection of light at the end face, ghost or flare or the like generates, which deteriorates quality of a picture image. Accordingly, light shading performance at the end face, low reflectivity, and low surface glossiness become important. In general, a resin film impregnated with a black pigment is used as a substrate in many cases, to absorb light injected to the end face and shade it. However, in PATENT LITERATURES 2 and 3, although a resin film impregnated with a black pigment such as carbon black is used as a substrate, since the resin film is thick, it can only be said that, the black pigment having light shading performance can be added sufficiently, and reflection of light at the end face can be suppressed. In the case of a thinner film, there is a problem of losing light shading performance at the diaphragm surface or the end face, because content of the black pigment for obtaining a good film becomes low in film manufacturing.
As explained above, conventionally, in applications requiring heat resistance, it has been inevitable to use a heavier metal thin plate, that is, a metal thin plate composed of SUS, SK material, Al, Ti or the like, as compared with a resin film. Therefore, there have problems that torque or power consumption of a drive motor for driving a blade increases, or shutter speed cannot be raised, noise generates by contact of blades themselves, and further manufacturing cost increases for processing of black dying of the surface or a processed end face. Accordingly, new shutter blades or a fixed diaphragm and diaphragm blades of a diaphragm device for the light intensity adjusting module, having sufficient light shading performance, low reflectivity at the surface and processed end face, low surface glossiness, along with lightweight character, in addition to thickness of the light shading plate to be 25 μm or less, and superior heat resistance, have been required.